Seismic Performance of Multi-Chamber Irregular-Section CFST Columns with Different Structural Configurations

Literature Overview

The research by Cao Wanlin, Chen Xiangjia, Wu Haipeng, and Qiao Qiyun from Beijing University of Technology (2016, Structural Engineers, Vol. 32, No. 2, pp. 132-139) investigates the seismic behavior of irregular-section multi-chamber CFST columns, specifically focusing on the effect of the continuous versus discontinuous configuration of the vertical steel plates separating the chambers at the base level. Funded by the National Natural Science Foundation Major Research Plan (91315301) and NSFC Project (51178010), the study was motivated by the design of the Dalian International Trade Center, which features a pentagonal multi-chamber CFST mega-column. Four scaled specimens at a 1/7.5 scale were subjected to low-cycle reversed loading tests under two loading directions.

Core Technical Points and Interpretation

The multi-chamber configuration divides the interior of the large-diameter CFST column into multiple compartments using vertical steel plates (diaphragms). This internal partitioning serves to improve the confinement effect of the steel tube on the concrete core, particularly in large-diameter columns where the concrete core tends to spall prematurely under axial compression. The two configurations studied are: (1) continuous vertical plates extending through the base, and (2) discontinuous vertical plates with a gap at the base level.

The key finding is that the continuous configuration provides higher bearing capacity, better ductility, and greater energy dissipation capacity, but exhibits significant directional asymmetry in seismic performance. The discontinuous configuration shows slightly lower capacity but more uniform behavior across loading directions. This trade-off is critical for structural design in seismic regions where the direction of ground motion is unpredictable.

Process and Standards Analysis

The fabrication of multi-chamber CFST columns involves welding the vertical steel plates inside the steel tube before concrete placement. This internal welding operation is technically challenging due to the confined working space, limited access for welding equipment, and the difficulty of ensuring full penetration welds. The weld quality at the junction between the vertical plates and the steel tube wall is a critical factor in the overall seismic performance.

From a welding metallurgy perspective, the vertical plates are typically made from the same grade as the outer tube (e.g., Q345 or Q390), and the welds must be designed to match the base metal strength. The welding procedure should include preheating for thicker plates, controlled interpass temperatures, and post-weld inspection using ultrasonic testing (UT) or phased array ultrasonic testing (PAUT) to detect internal defects such as lack of fusion, porosity, and slag inclusions.

The relevant standards include JGJ 8 (Technical Specification for Concrete-Filled Steel Tubular Structures), GB 50011 (Code for Seismic Design of Buildings), and GB 50661 (Steel Structure Welding Code). The seismic performance requirements for CFST columns are governed by the ductility and energy dissipation criteria specified in these standards, which must be satisfied to ensure adequate seismic resistance.

Integration with Engineering Practice

In the context of the Dalian International Trade Center, the mega-column is a critical structural element that supports the entire building above. The choice between continuous and discontinuous vertical plate configurations has direct implications for the seismic design philosophy. The continuous configuration offers superior strength and ductility but introduces directional bias, which may be problematic if the seismic hazard is predominantly unidirectional. The discontinuous configuration provides more balanced behavior at the cost of slightly reduced capacity.

For engineering practice, the selection should be guided by a comprehensive seismic hazard analysis that considers the predominant ground motion directions at the site. If the site is in a region with predominantly unidirectional seismic hazard (e.g., near a single fault), the continuous configuration may be acceptable with appropriate design adjustments. For sites with multidirectional hazard potential, the discontinuous configuration may be preferred for its uniform behavior.

Key Questions and Reflections

The study raises an important question about the practical implications of directional asymmetry in seismic design. Current seismic design codes generally assume isotropic loading conditions, but the continuous configuration introduces anisotropic behavior that may not be adequately captured by standard design procedures. Engineers must consider whether the design code provisions account for this directional effect or whether additional analysis is required.

Another consideration is the effect of the vertical plate configuration on the concrete placement and compaction process. The internal plates divide the concrete core into separate compartments, which can affect the uniformity of concrete fill and the potential for voids or honeycombing. Quality control during concrete placement must ensure complete and uniform fill in each compartment, as voids would significantly reduce the confinement effect and compromise seismic performance.

Study Insights and Implications

This research provides valuable experimental data on the seismic behavior of multi-chamber CFST columns, which are increasingly used in large-scale commercial and infrastructure projects. The findings highlight the importance of internal structural configuration in determining seismic performance and provide engineers with practical guidance for design decisions. The study also demonstrates the effectiveness of scaled model testing as a research methodology for investigating the behavior of full-scale structural elements. For future work, the authors implicitly suggest that further research should explore hybrid configurations that combine the strengths of both continuous and discontinuous designs, as well as the long-term performance under multi-hazard loading conditions.